The present invention relates to a viscous material pump for pumping slurry materials and the like and, more particularly, to means and to a method for precisely measuring the delivery volume of the viscous material pump.
Viscous material pumps for conveying and rating pasty materials, for example slurries or the like, are known in various embodiments. It is further known to use self-priming positive displacement piston pumps. The conveying piston of at least a conveying cylinder is connected to the drive piston of a hydraulic drive cylinder, wherein the end positions of the drive piston are sensed by end position transmitters or by means of directional valves to generate control signals for a valve operable to selectively connect the conveying cylinder to a supply or delivery line. The supply line regularly includes a supply means, for example a screw pump, to deliver the material towards the conveying cylinder.
The efficiency of a pump of this type not only depends on the theoretical delivery volume of the conveying cylinder and its cycle time, but further depends on the percent fill possibly being reached during each suction stroke. It is known to measure the delivery volume of this type of pump using a method based on inductivity. However, this type of measurement relies on a minimum flow rate and a minimum volume of liquid in the material. For example, U.S. Pat. No. 5,106,272 discloses a measuring system indicating during each pumping stroke when the material begins to flow. The actual delivery or pumping stroke time is shorter than the time needed for the overall pumping stroke of the conveying piston such that the ratio between both theses values indicates the percent fill of the conveying cylinder during the preceding filling stroke. Summing up the individual filling volumes with respect to time results in an indication of the actual delivery volume. The known method suffers from the drawback that a valve determines or controls when the material begins to flow, which valve prematurely opens when a low or zero counter pressure prevails in the delivery line, thus not permitting the obtaining of accurate measuring values of the viscous material pump.
In other known systems, the viscous material pump and the supply means operate independently from each other. It is known to match the delivery volumes with respect to each other by undertaking a visual control. An adjustment of the supply means is performed by locally adjusting a mechanical throttle valve, for example, or by a remote control by means of a potentiometer and proportional valve. However, this system is not suited to obtain a maximum efficiency of the viscous material pump.